The FBI is going to conduct its own investigation into the death of a 13-year-old who was shot after police mistook the boy's pellet gun for an assault rifle, the Sonoma County Sherriff said today.

"The Sheriff will cooperate fully with the FBI and welcomes their participation," the Sheriff's office said in a statement. "The Sheriff also wants to express his thankfulness to the community for how peaceful and respectful the memorials and protests have been in the aftermath of this incident."

Any Lopez's death Tuesday has triggered outrage and grief among hundreds of residents of Santa Rosa, Calif., who marched three miles Wednesday night from Santa Rosa City Hall to the field where Lopez was shot.

Hundreds more attended a vigil Thursday night, while more than 100 middle and high school students, among them Lopez's friends, marched to the Sherriff's Office on Friday chanting, "No justice, no peace!" and waving banners.

"Andy was my friend. We had to do this for him," Steven Morrison Jr., a middle school student told ABC station KGO-TV in San Francisco.

"I don't know what happened to those cops, but that was wrong," said another middle school student, Jamie Cutforth.

At around 3:14 on Tuesday afternoon, two deputies riding in a marked patrol vehicle noticed Lopez holding a pellet gun that bore striking resemblance to an AK-47 assault rifle, replete with black body, ammunition magazine and brown butt and grip.

Santa Rosa police said Lopez, who was wearing a hooded sweatshirt, had his back turned toward the officers and they did not realize he was a boy. The deputy twice ordered the Lopez to "drop the gun," but said he instead raised and pointed it in their direction.

Officers fired several rounds from their handguns at Lopez, who fell to the ground, landing on top of the rifle, a police statement said. He was not moving when the officers placed handcuffs on him, and was pronounced dead at the scene by paramedics.

Deputies also found a plastic hand gun in the boy's waistband when they searched him, the Sonoma Sherriff's office said in a statement. The release also contained a picture of the replica assault weapon.

Lopez was shot seven times, with the two fatal shots being fired into the teen's right hip and right side of his chest, according to a preliminary autopsy report released Thursday.

"The deputy's mindset was that he was fearful that he was going to be shot," Santa Rosa police Lt. Paul Henry said Wednesday at a news conference.

But residents of the Northern California community have questioned the actions of the deputies, who have since been placed on administrative leave.

"Nobody should die for a misunderstanding, especially not a young boy who hasn't even started his life. It's just really sad knowing that," Viviany Diaz Agirra Torres, 17, told The Associated Press.

Police released a timeline of the incident Thursday that indicated only 10 seconds passed between the time officers called to report a suspicious person, to the time they called dispatch again to report fired shots, the AP reported.

Andy Lopez has been described as popular, smart and capable by school administrators. His father, Rodrigo Lopez, told the Press Democrat that the pellet gun belonged to one of his son's friends.

"I told him what I tell him every day," he said of his last encounter with his son. "Behave yourself."